1. Field of the Invention
The invention is directed to a spark plug for an internal combustion engine and an internal combustion engine.
2. Description of the Related Art
Spark plugs are used for electric ignition of a fuel mixture to be burned in an internal combustion engine. Between a center electrode and a ground electrode of a spark plug there is a spark gap in which an electric ignition spark can be formed for igniting the fuel mixture. A basic distinction is made between spark plugs with a hooked ground electrode and spark plugs with an annular ground electrode. DE 10 2008 061 242 A1 shows an internal combustion engine with a spark plug having a hooked ground electrode, the spark gap extending axially between one end of the center electrode and one end of the hooked ground electrode viewed in axial direction of the center electrode. A spark plug with an annular ground electrode is known from DE 101 45 944 A1. In this case, the spark gap extends between the center electrode and the ground electrode in radial direction around the center electrode.
The surfaces of the ground electrode and center electrode of a spark plug between which an electric ignition spark is formed for igniting the fuel mixture are fabricated from noble metal or coated with noble metal. This noble metal is subject to wear when an ignition spark is generated.
As a result of this wear, the spark gap between the center electrode and the ground electrode increases in size and, as the spark gap becomes larger, more ignition energy must be applied to form the ignition spark. When the dimensions of the spark gap have exceeded a critical quantity, the spark plug must be exchanged.